Why do you say that? When dissolved in water, metabisulfite forms bisulfite ion and they are the same thing. In amateur darkroom formulae I doubt anyone ever used pure sodium bisulfite in dry form as an ingredient; it's a misnomer.

When Kodak sold chemicals a mixture of sodium bisulfite and sodium metabisulfite was sold as sodium bisulfite. If you look at the MSDS for sodium bisulfite it is listed as 58 - 99% sodium bisulfite and 0 - 42% sodium metabisulfite. Pure sodium bisulfite is sold as a 40 - 45% solution rather than as a solid.

Kodak recommended using the same amount regardless of which chemical the formula mentioned.